Mechanics

F150 CHARGING PROBLEM.

2004 Ford F-150

Electrical problem
2004 Ford F150 V8 Four Wheel Drive Automatic 120k miles

I have a 2004 F-150. I was driving it when the battery light came on. After a while I saw the voltage meter drop quickly and when I shut off truck battery was dead. If I charged battery with cables truck would run off battery until charge ran out. Replaced alternator, problem seemed fixed but light remained on. While driving on highway 1000 k later saw needle dropping while I was at low rpm. Got truck to 3000 rpm needle returned to normal. About 3000k later same thing happened and needle again shot back up but only when I put rpm to 3000. If voltage needle drops and I don't hit 3000 rpm truck will die. I can keep truck charged by pulling over and hitting high rpms, as soon as I hit 3000 rpm needle returns and stays at normal. Please help
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JohnLundrigan
August 23, 2010.



I would start by having the alt and regulator rechecked. If that is good, then I would start checking fuseable links between the alt and the battery.